Sensor for contactless determination of an angle of rotation of a rotatable structural element

Abstract: The sensor comprises: a rotor 10 constructed of a rotating shaft 7 and a semicylindrical rotating core 9 mounted on the shaft 7; and, a stator coaxially arranged with the rotor 10 surrounded by a pair of annular stator coils 11, 13 arranged one above the other in an axial direction of the rotor 10. A yoke member for the coils 11, 13 is provided with magnetic-substance plates 19, 21, 23, 25. The plates 19, 21 for the coil 11 have halves 19A, 21A their inner peripheral portions protrude radially inwardly to approach the rotor 10, while the remaining plates 23, 25 for the coil 13 have halves 23A, 25A their inner peripheral portions protrude radially inwardly to approach the rotor 10. The halves 23A, 25A are oppositely disposed from the halves 19A, 21A to have the coils 11, 13 be opposite to each other in phase of the inductance when the rotor 10 rotates.

Description: The present invention relates to a sensor for contactless determination of an angle of rotation of a rotatable structural element according to the preamble of claim 1. Sensors are classified into two basic types, i.e., contact-type ones and contactless-type ones. A typical one of the contact-type is constructed of a resistor element and a rotating brush kept in contact with the resistor element. The contact-type sensors are simple in construction and low in manufacturing cost. However, any of the contact-type sensors has the disadvantage in being shortened in service life due to wear on contact areas of its components. On the other hand, the contactless-type sensors are free from the above disadvantage. A typical one of the contactless-type sensors is constructed of: a stator provided with a pair of coils; and, a rotor provided with at least one magnetic-substance portion which is so arranged as to vary a distance between the magnetic-substance portion and each of the coils when the rotor rotates to vary its angle of rotation relative to the stator. In the typical one of the contact-less type sensors, the angle of rotation, i.e., angular displacement of the rotor is determined through detection of variations in voltage in a circuit caused by variations in inductance in the pair of the coils forming the circuit. As for the contactless-type sensors, Japanese Patent Laid-Open No. Sho 59-174702 discloses an concrete example of the sensors, in which a stator is constructed of: a cylindrical yoke member; and, a pair of coils oppositely disposed from each other in a diametrical direction on a line perpendicular to a central axis of the cylindrical yoke member. In the above example, a rotor of the sensor is constructed of a semicylindrical magnetic-substance element which is rotatable on the central axis of the cylindrical yoke member. In operation, the rotor assuming the semicylindrical shape is detected in angular displacement by the pair of the coils in which the angular displacement of the rotor is converted into variations in conductances of the coils, i.e., variations in voltage in a circuit comprising the coils, which permits the example of the sensor to determine the angular displacement of the rotor through detection of the variations in voltage. This example, i.e., the conventional sensor for the contactless determination of the angular displacement of the rotor has the disadvantage that the stator is too complex in manufacturing. In other words, in the stator of the conventional sensor, the pair of the coils are disposed on an inner peripheral surface of the cylindrical yoke member so as to be oppositely, disposed from each other. In manufacturing of such coils: first, each of the coils is formed; and, the thus formed coils are disposed in predetermined positions on the inner peripheral surface of the yoke member through assembly operations. In this case, since the conventional sensor is directly influenced in its determination accuracy by variations in installation positions of the coils, it is necessary for the conventional sensor to perform the positioning operations or assembly operations of the coils with very high accuracy, which impairs the conventional sensor in productivity. WO - A - 92/14121, which forms the starting point of the present invention, discloses two different embodiments of a sensor for contactless determination of an angle of rotation. The first embodiment comprises non-circular stator coils interacting with an asymmetrical rotor element. The second embodiment provides two angular stator coils arranged coaxially with respect to an asymmetrical rotor element. However, any additional magnetic-circuit member associated to the stator coils is not provided. EP - A - 0 365 758 describes a sensor for contactless determination of an angle of rotation, wherein an asymmetrically shaped rotor element can rotate within a coil arrangement including two coils spaced axially and arranged coaxially. Further, a hollow shielding cylinder with two segmental openings is provided between the rotor element and the coil arrangement. This results in an increase of the distance between the coil and the rotor element, thus limiting the accuracy and sensitivity of the sensor. Additional magnetic-circuit members associated to the coils are not provided. Object of the present invention is to improve the sensor with the above-mentioned features in that a high accuracy in determination of an angle of rotation can be obtained. The above object is achieved by a sensor according to claim 1. Preferred embodiments are subject of the subclaims. Especially, a sensor is provided which comprises: a rotor provided with a magnetic-substance element arranged asymmetrically with respect to an axis of rotation of the rotor; a first and a second annular stator coil arranged coaxially with respect to the rotor; a magnetic-circuit member forming a yoke or core means for each of the first and the second annular stator coil; the magnetic-circuit member for the first stator coil assuming an asymmetric shape with respect to the axis of rotation of the rotor so as to approach the magnetic-substance element of the rotor only when the angle of rotation of the rotor is in a first angular range, whereby the magnetic-substance element of the rotor functions as a part of a magnetic circuit of the first stator coil; and the magnetic-circuit member for the second stator coil assuming an asymmetric shape with respect to the axis of rotation of the rotor so as to approach the magnetic-substance element of the rotor only when the angle of rotation of the rotor is in a second angular range outside the first angular range, whereby the magnetic-substance element of the rotor functions as a part of a magnetic circuit of the second stator coil. Consequently, in the present invention having the above construction, since the first angular range in which the magnetic-substance element of the rotor functions as a part of the magnetic circuit of the first stator coil is outside the second angular range in which the magnetic-substance element of the rotor functions as a part of the magnetic circuit of the second stator coil, the first and the second stator coil have their inductances vary in alternating phase patterns as the rotor rotates, which enables the sensor to detect the angle of rotation of the rotatable structural element based on the differences in induction between these stator coils. Preferably, each of the stator coils assumes an annular shape coaxially arranged with respect to the axis of rotation of the rotor. In this case, it is possible to manufacture each of the stator coils in an easy manner through a simple operation, for example, by winding a wire on an annular bobbin. In addition, assembly operations of the stator coils in the sensor are simply accomplished by coaxially arranging the stator coils with respect to the rotor. Consequently, it is possible to perform positioning operations of the stator coils with high accuracy in a simple manner through the assembly operations, for example, by inserting the bobbins wound with the stator coils into a cylindrical casing of the sensor after insertion of the rotor into the casing. Further, in the present invention having the above construction, a detecting accuracy of the sensor is directly influenced by asymmetrical shapes of the stator coils and positions of the stator coils relative to each other. As for the magnetic-circuit forming members, it is possible to manufacture them with high accuracy in shape from magnetic-substance plates through press workings or through sintering processes of ferrous-metal powders. In assembly operations of the magnetic-circuit forming members, there are employed a plurality of positioning means which enable all the magnetic-circuit forming members or plates, bobbins and the rotor to be properly positioned relative to each other in the casing of the sensor by simply inserting them in this order into the casing. As it is clear from the above, according to the present invention, it is possible to easily manufacture the sensor excellent in accuracy in contactless determination of the angle of rotation of the rotatable structural element. Fig. 1 is a longitudinal sectional view of an essential part of a sensor of an embodiment of the present invention; Fig. 2A is a cross-sectional view of the sensor of the present invention, taken along the line X-X of Fig. 1; Fig. 2B is a cross-sectional view of the sensor of the present invention, taken along the line Y-Y of Fig. 1; Fig. 3 is an exploded perspective view of the sensor of the present invention shown in Fig. 1; Fig. 4 is a diagram of an electrical circuit for the sensor of the present intention shown in Fig. 1; Fig. 5 is a graph illustrating the relationship between the variation of output voltage and the angle of rotation measured in the circuit shown in Fig. 4; Fig. 6 is a graph illustrating the relationship between the output voltage and the angle of rotation in an angular range in which the output voltage appears to be linear; Fig. 7 is a longitudinal sectional view of an essential part of a second embodiment of the sensor of the present invention, illustrating the stator portion of the sensor; Fig. 8 is a longitudinal sectional view of an essential part of a third embodiment of the sensor of the present invention, illustrating the stator portion of the sensor; Fig. 9 is a perspective view of an essential part of the third embodiment of the sensor of the present invention, illustrating in arrangement the magnetic-substance plates or cores and the electrically conductive plates for performing the magnetic shielding of the stator coils in the third embodiment; Fig. 10 is an exploded perspective view of another embodiment of the sensor of the present invention, illustrating the positioning means provided in the sensor of the present invention; Fig. 11 is an exploded perspective view of further another embodiment of the sensor of the present invention, illustrating the positioning means provided in the sensor of the present invention; and Fig. 12 is an exploded perspective view of the further another embodiment of the present invention shown in Fig. 11, illustrating the assembly operations thereof. DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinbelow, the present invention will be described in detail with reference to the accompanying drawings. In a first embodiment of the present invention shown in Figs. 1 to 3, a sensor for contactless determination of an angle of rotation of a rotatable structural element according to the present invention is provided with a casing 1 which assumes a hollow cylindrical shape having at least its outer peripheral wall portion made of a magnetic substance. As is clear from Fig. 1, a yoke segment 100 made of a magnetic substance is fitted in the casing 1. Coaxially mounted in the casing 1 through a pair of bearings 3, 5 is a rotating shaft 7 which is made of a non-magnetic substance and rotatable relative to the casing 1. Fixedly mounted on a portion of the rotating shaft 7 inside the casing 1 is a rotating core member 9. The core member 9 is made of a magnetic substance and assumes a semicylindrical shape axially extending parallel with the rotating shaft 7 to have its center axis coincide in position with that of the rotating shaft 7. A rotor 10 of the sensor of the present invention is constructed of the rotating shaft 7 and the rotating core member 9. Incidentally, the rotating core member 9 functions as a core member of each of a first stator coil 11 and a second stator coil 13 which are deferred until later. The stator coils 11, 13, each of which assumes an annular shape, are fitted in the casing 1 so as to surround the rotor 10. The stator coils 11 and 13 are wound on annular bobbins 15 and 17, respectively. The bobbins 15, 17 are fitted in the yoke segment 100 having fitted in the casing 1. In other words, the bobbins 15, 17 have their outer peripheral surfaces abut on the inner peripheral surface of the yoke segment 100 fitted in the casing 1, and, therefore are coaxially arranged with respect to an axis of rotation of the rotor 10 so as to overlap each other in a direction parallel to the axis of rotation of the rotor 10. Fixedly mounted on opposite axial sides or surfaces (i.e., an upper and a lower surface, as viewed in Fig. 1) of the bobbin 15 of the first stator coil 11 are a pair of magnetic-substance plates 19, 21 each of which assumes a partially-flanged annular shape. These magnetic-substance plates 19, 21 have their outer peripheral surfaces abut on the inner peripheral surface of the yoke segment 100 fitted in the casing 1. A yoke member for the first stator coil 11 is constructed of the pair of the magnetic-substance plates 19, 21 and the yoke segment 100. In the same manner as described above, a pair of magnetic-substance plates 23, 25 each of which assumes a partially-flanged annular shape are fixedly mounted on opposite axial sides or surfaces (i.e., an upper and a lower surface, as viewed in Fig. 1) of the bobbin 17 of the second stator coil 13. These magnetic-substance plates 23, 25 have their outer peripheral surfaces abut on the inner peripheral surface of the yoke segment 100 fitted in the casing 1. A yoke member for the second stator coil 13 is constructed of the pair of the magnetic-substance plates 23, 25 and the yoke segment 100. Incidentally, an open end (i.e., an upper end, as viewed in Fig. 1) of the casing 1 is closed with a flanged disc-like member 101. As is clear from Fig. 2A, an inner peripheral portion of each of the magnetic-substance plates 19, 21 forming a part of the yoke member of the first stator coil 11 is half constructed of a radially inwardly protruding portion and half of a radially outwardly recessed portion. Namely, the radially inwardly protruding portion of the magnetic-substance plate 19 is denoted by the reference numeral 19A, and that of the magnetic-substance plate 21 is denoted by the reference numeral 21A, as shown in Fig. 1. Each of the protruding portion 19A, 21A has an angular range (i.e., a central angle) of 180° with respect to the axis of rotation of the rotor 10, and has its inner-end portion flanged to axially extend parallel to the axis of rotation of the rotor 10. Namely, as is clear from Fig. 1, the thus flanged inner-end portion of each of the protruding portions 19A, 21A radially inwardly extends from an inner peripheral surface of the annular bobbin 15, and then axially extends parallel to the same so as to be adjacent to the inner peripheral surface of the annular bobbin 15. As is clear from the above description and from Fig. 2A, the remaining inner peripheral portion, i.e., each of the radially outwardly recessed portions of the magnetic-substance plates 19, 21: has a central angle of 180°; has its inner-end portion not flanged so to be smaller in area of its inner peripheral surface than the flanged inner-end portion of each of the radially inwardly protruding portions 19A, 21A; and, has its inner-end portion so disposed as to permit the rotor 10 to be closer to the inner peripheral surface of the bobbin 15 than to the inner-end portion. In a condition in which the rotor 10 rotates to have its rotating core member 9 reach a position shown in Figs. 1 and 2A so as to face the protruding portions 19A, 21A of the magnetic-substance plates 19, 21, an outer peripheral surface of the rotating core member 9 faces each of the inner peripheral surfaces of the protruding portions 19A, 21A through a minute clearance. As a result, a magnetic circuit as shown in alternate long and short dash line in Fig. 1 is formed around the first stator core 11 to permit the rotating core member 9 to function as a core element of the first stator coil 11. The same is true as to the second stator coil 13 as described later. On the other hand, in a condition in which the rotor 10 rotates to have its rotating core member 9 to reach the other side position shown in Fig. 2B, the rotating core member 9 is spaced far away from the protruding portions 19A, 21A of the magnetic-substance plates 19, 21. Consequently, any magnetic circuit is not formed as to the rotating core member 9, and, therefore the core member 9 does not function as a core element of the first stator coil 11. The same is true as to the second stator coil 13 as described later. Namely, as the rotor 10 rotates, the rotating core member 9 has its outer peripheral surface move alternately toward and away from the inner peripheral surfaces of the protruding portions 19A, 21A of the magnetic-substance plates 19, 21 so as to intermittently serve as the core element of the first stator coil 11, which causes the inductance of the stator coil 11 to vary. Incidentally, in order to obtain large variations of the inductance, it is necessary to increase in area the inner peripheral surfaces of the protruding portions 19A, 21A of the magnetic-substance plates 19, 21 and to increase an axial clearance between these protruding portions 19A and 21A. In order to increase in area the inner peripheral surfaces of the protruding portions 19A, 21A, it is necessary to increase in height h (i.e., axial length h) of each of the flanged inner-end portions of the protruding portions 19A, 21A. On the other hand, in order to increase the axial clearance between the protruding portions 19A and 21A, it is necessary to decrease the height or axial length h. Based on the above facts, it is found that a preferable value of the height h is approximately a quarter of an axial thickness (i.e., a vertical length, as viewed in Fig. 1) of the first stator coil 11. On the other hand, as for the remaining magnetic-substance plates 23, 25 forming a part of a yoke member of the second stator coil 13, an inner peripheral portion of each of the magnetic-substance plates 23, 25 is half constructed of a radially inwardly protruding portion and half of a radially outwardly recessed portion. Namely, the radially inwardly protruding portion of the magnetic-substance plate 23 is denoted by the reference numeral 23A, and that of the magnetic-substance plate 25 is denoted by the reference numeral 25A, as shown in Fig. 1. Each of the protruding portion 23A, 25A has an angular range (i.e., a central angle) of 180° with respect to the axis of rotation of the rotor 10, and has its inner-end portion flanged to axially extend parallel to the axis of rotation of the rotor 10. Namely, as is clear from Fig. 1, the thus flanged inner-end portion of each of the protruding portions 23A, 25A radially inwardly extends from an inner peripheral surface of the annular bobbin 17, and then axially extends parallel to the same so as to be adjacent to the inner peripheral surface of the annular bobbin 17. As is clear from the above description and from Figs. 1 and 2B, the remaining inner peripheral portion, i.e., each of the radially outwardly recessed portions of the magnetic-substance plates 23, 25: has an angular range (i.e., a central angle) of 180°; has its inner-end portion not flanged to be smaller in area of its inner peripheral surface than the flanged inner-end portion of each of the radially inwardly protruding portions 23A, 25A; and, has its inner-end portion so disposed as to permit the rotor 10 to be closer to the inner peripheral surface of the bobbin 17 than to the inner-end portion. Incidentally, a semicircular shape shown in dotted line in Fig. 2B is of the inner peripheral surface of the annular bobbin 17, illustrating the position of the inner peripheral surface. As is clear from Figs. 2A and 2B, the protruding portions 19A, 21A of the magnetic-substance plates 19, 21 and those 23A, 25A of the magnetic-substance plate 23, 25 do not overlap each other. In other words, the former 19A, 21A and the latter 23A, 25A are 180 degrees out-of-phase in arrangement relative to each other. Consequently, as the rotor 10 rotates, the stator coils 11, 13 vary in inductance so as to have their induced voltages be 180 degrees out-of-phase relative to each other. Fig. 4 shows a diagram of an electric circuit used in the sensor of the embodiment of the present invention. The circuit comprises: a rectifier circuit 27 for rectifying a tap voltage V B of the stator coil 11 (or 13); and, an amplifier circuit 29 for amplifying an output voltage issued from the rectifier circuit 27. The stator coils 11, 13 are connected in series with each other, applied across which coils 11, 13 is an a.c. voltage Vin. On the other hand, the tap voltage VB of the stator coil 11 (or 13) varies as the rotor 10 rotates. The tap voltage V B is rectified through the rectifier circuit 27 and amplified through the amplifier circuit 29 from which an output or detected voltage Vout is issued. As shown in Fig. 6, the sensor of the embodiment of the present invention is substantially linear in output characteristic within a predetermined range of the angle of rotation of the rotor 10, i.e., the output voltage of the sensor is represented by a substantially linear function of the angle of rotation of the rotor 10 in the predetermined range. of the angle of rotation. The output characteristics, i.e., output voltage Vout (shown in Fig. 4) issued from output terminals of the amplifier circuit 29 of the sensor of the present invention is obtained by applying the a.c. voltage Vin to the circuit of the sensor. The a.c. voltage Vin is a sin wave (oscillation frequency: 3.7 KHz) with an amplitude of 1 Vp-p a null level of which is 2 V. Variations of the a.c. voltage Vout during a full revolution of the rotor 10 relative to the stator coils 11, 13 are shown in the graph of Fig. 5. As is clear from the output characteristics shown in Fig. 5, a value of the a.c. voltage Vout increases in an angular range of from 0° to 180°, and decreases in the remaining angular range of from 180° to 360°. In practice, useful ones of the angular range of the graph shown in Fig. 5 are preferably: one around an angle of 90° (for example, one of from 10° to 170°, in which the graph is substantially linear); or one around an angle of 270° (for example, one of from 190° to 350°, in which the graph is substantially linear). Fig. 7 shows a second embodiment of the present invention, which will he now described with reference to the drawings. The construction of the second embodiment of the present invention is the same as that of the first embodiment of the present invention descried above, with the exception of the construction of the rotor 10. Namely, in the rotor of the second embodiment of the present invention, two parallel-extending core members, i.e., a first core member 31 and a second core member 33, each of which is constructed of a semicircular magnetic-substance plate, are fixedly mounted on the rotating shaft 7 so as to be perpendicular to the shaft 7. Each of the core members 31, 33 has its center axis coincide in position with the axis of rotation of the rotating shaft 7, and overlap each other in a direction parallel to the axis of rotation of the rotating shaft 7. As shown in Fig. 7, in a condition in which the first core member 31 reaches a position in which an outer peripheral portion of the core member 31 is oppositely disposed from each of the protruding portions 19A, 21A of the magnetic-substance plates 19, 21 (which form a part of the yoke member of the first stator coil 11) through a minute clearance in a direction parallel to the axis of rotation of the rotating shaft 7, the outer peripheral portion of the core member 31 is axially sandwiched between the protruding portions 19A, 21A through the minute clearances, which enables the first core member 31 to serve or function as a core element of the first stator coil 11. Namely, as shown in alternate long and short dash line in Fig.7, a magnetic circuit passing through the magnetic-substance plates 19, 21, yoke segment 100 and the first core member 31 is formed around the first stator coil 11. On the other hand, as for the second core member 33, in a condition in which the second core member 33 reaches a position in which an outer peripheral portion of the core member 33 is oppositely disposed from each of the protruding portions 23A, 25A (shown in Fig. 1) of the magnetic-substance plates 23, 25 of the second stator coil 13 through a minute clearance in a direction parallel to the axis of rotation of the rotating shaft 7, the outer peripheral portion of the core member 33 is axially sandwiched between the protruding portions 23A, 25A through the minute clearances, which enables the second core member 33 to serve or function as a core element of the second stator coil 13. Namely, as is in the case of the magnetic circuit around the first stator coil 11 shown in alternate long and short dash line in Fig. 7, another magnetic circuit passing through the magnetic-substance plates 23, 25, yoke segment 100 and the second core member 33 is formed around the second stator coil 13. Consequently, as the rotor 10 rotates, the stator coils 11, 13 vary in inductance so as to have their induced voltages be 180 degrees out-of-phase relative to each other, because the protruding portions 19A, 21A of the magnetic-substance plates 19, 21 (i.e., the former) and those 23A, 25A of the magnetic-substance plate 23, 25 (i.e., the latter) do not overlap each other so as to permit the former to be 180 degrees out-of-phase in arrangement relative to the latter. Now, a third embodiment of the present invention will be described with reference to Fig. 8. In the third embodiment of the present invention, a rotating shaft 47 made of a non-magnetic substance is rotatably mounted in a casing 41 through bearings 43, 45 so as to be coaxially arranged with the casing 41. Fixedly mounted on an intermediate portion of the rotating shaft 47 in the casing 41 is a rotating yoke 49 which is made of a magnetic substance and assumes a semicircular plate form. The rotating yoke 49 has its center axis coincide in position with an axis of rotation of the rotating shaft 47, so that a rotor 50 is constructed of the rotating yoke 49 and the rotating shaft 47. Incidentally, the rotating yoke 49 functions as a yoke member of each of stator coils 51, 53 which will be described later. These two stator coils 51, 53, each of which assumes an annular shape, are fixedly mounted in the casing 41 so as to sandwich the rotating yoke 49 therebetween through minute clearances in a direction parallel to the axis of rotation of the rotating shaft 47 or of rotor 50. The stator coils 51 and 53 are wound on annular bobbins 55 and 57, respectively. The bobbins 55, 57 have their outer peripheral surfaces fitted to the inner peripheral surface of the yoke segment 200 having fitted in the casing 41. The thus fitted bobbins 55, 57 have their center axes coincide in position with the axis of rotation of the rotor 50, and overlap each other in a direction parallel to the axis of rotation of the rotor 50 within the casing 41. As shown in Fig. 9, a semicylindrical core member 59 is fitted to the inner peripheral surface of the annular bobbin 55 of the stator coil 51. In construction, an upper surface of the core member 59 (as viewed in Fig. 8) is brought into area contact with an lower surface of a mounting flange member 201. On the other hand, the other side, i.e., a lower surface of the core member 59 faces the rotating yoke 49 through a minute clearance when the rotating yoke 49 reaches a position in which the rotating yoke 49 is oppositely disposed from the core member 59. As described later, when the rotating yoke 49 reaches a position in the vicinity of the semicylindrical core member 59, a yoke element for the stator coil 51 is constructed of the rotating yoke 49, core member 59, yoke segment 200 and the casing 41. On the other hand, a conductive plate 61 is made of electrically conductive materials, for example such as copper and the like, and assumes a semicircular dish shape as shown in Fig. 9. The conductive plate 61 is fixedly mounted on a half area of a lower surface (as viewed in Fig. 8) of the annular bobbin 55, which half area is free from the core member 59 as is clear from Fig. 9. In action, the conductive plate 61 prevents the magnetic flux of the stator coil 51 from entering a lower half of the interior of the casing 41, contained in which lower half is the other stator coil 53. As for the stator coil 53, the same described above is true in construction and action. Namely, a semicylindrical core member 63 is fitted to the inner peripheral surface of the annular bobbin 57 of the stator coil 53. In construction, a lower surface of the core member 63 (as viewed in Fig. 8) is brought into area contact with a bottom inner surface of the casing 41. On the other hand, the other side, i.e., an upper surface of the core member 63 faces the rotating yoke 49 through a minute clearance when the rotating yoke 49 reaches a position in which the rotating yoke 49 is oppositely disposed from the core member 63. As described later, when the rotating yoke 49 reaches a position in the vicinity of the semicylindrical core member 63, a yoke element for the stator coil 53 is constructed of the rotating yoke 49, core member 63, yoke segment 200 and the casing 41. On the other hand, an electrically conductive plate 65, which assumes a semicircular dish shape as shown in Fig. 9, is fixedly mounted on a half area of an upper surface (as viewed in Fig. 8) of the annular bobbin 57, which half area is free from the core member 63 as is clear from Fig. 9. In action, the conductive plate 65 prevents the magnetic flux of the stator coil 53 from entering an upper half of the interior of the casing 41, contained in which upper half is the stator coil 51. In the third embodiment of the present invention having the above construction, when the rotor 50 rotates to reach a position in which the rotating yoke 49 of the rotor 50 is placed close to the core member 63 of the stator coil 53, as is shown in alternate long and short line in fig. 8, a magnetic circuit passing through the rotating yoke 49, annular bobbin 57, yoke segment 200, casing 41 and the core member 63 is formed around the stator coil 53, so that the rotating yoke 49 functions as a yoke element for the stator coil 53. At this time, the magnetic flux of the stator coil 51 is prevented from entering the lower half of the interior of the casing 41 by means of the conductive plate 61. Consequently, there is no fear that the magnetic flux of the stator coil 51 passes through the rotating yoke 49. The same is true as to the magnetic flux of the stator coil 53 when the rotating yoke 49 reaches the other side position in which: the rotating yoke 49 now functions as a yoke element of the stator coil 51, so that the magnetic flux of the stator coil 53 is now prevented from entering the upper half of the interior of the casing 41 by means of the conductive plate 65, contained in which upper half is the stator coil 51. Consequently, there is no fear that the magnetic flux of the stator coil 53 passes through the rotating yoke 49 functioning now as the core element of the stator coil 51. When the rotor 50 rotates, the rotating yoke 49 functions as alternately the yoke element of the stator coil 51 and that of the stator coil 53. Consequently, the stator coils 51, 53 are 180° out-of-phase in inductance relative to each other. As a result, it is possible to detect an angle of rotation of the rotor 10 by the use of an electrical circuit similar to that of Fig. 4. Incidentally, in the first embodiment of the present invention described above with reference to Figs. 1 to 6, the rotating core 9 member may assume a hollow shape, provided that the core member 9 is asymmetrically arranged with the axis of rotation of the rotor 10. Further, although a range of the magnetic circuit constructed of the yoke member of the first embodiment is approximately 180°, it is also possible to properly decrease in width each of the protruding portions 19A, 21A, 23A, 25A of the yoke members or magnetic-substance plates 19, 21, 23, 25 when an effective detection range of the first embodiment of the sensor of the present invention is less than 180°. Now, positioning means provided between the components of the sensor of the present invention will be described. Fig. 10 shows a fourth embodiment of the sensor of the present invention, which substantially corresponds in construction to the first embodiment of the present invention shown in Fig. 3, with the exception of the provisions of the positioning means. The fourth embodiment of the present invention will be described with reference to Fig. 10. As described below in detail, the positioning means are provided between: the magnetic-substance plates 19, 21, 23, 25 and the annular bobbins 15, 17; the annular bobbins 15 and 17; and, the annular bobbins 15, 17 and the casing 1. Namely, first, as already described in the above, the protruding portions 19A, 21A and 23A, 25A (i.e., halves) of the magnetic-substance plates 19, 21 and 23, 25 are fitted to the inner peripheral surfaces of the annular bobbins 15 and 17, respectively. Consequently, each pair of the protruding portions 19A, 21A and 23A, 25A function as the part of the yoke member of each of the stator coils 11, 13, and further function as the positioning means for positioning each of the annular bobbins 15, 17. The remaining halves of the magnetic-substance plates 19, 21 and 23, 25 are not provided with any protruding portion, and are largely notched or recessed to form recessed portions 19B, 21B and 23B, 25B. On the other hand, the annular bobbins 15 and 17 are provided with semicircular protruding portions 15A and 17A in their axial surfaces, respectively. The protruding portions 15A and 17A are fitted in the recessed portions 19B, 21B and 23B, 25B, respectively, so that the magnetic-substance plates 19, 21 and 23, 25 are positioned relative to the annular bobbins 15 and 17 through the positioning means constructed of the protruding portions 15A, 17A of the annular bobbins 15, 17 and the recessed portions 19B, 21B, 23B, 25B. Incidentally, in place of the semicircular protruding portions 15A, 17A, it is also possible to form grooves in positions corresponding to those of the protruding portions 15A, 17A in the bobbins 15, 17, and to form protruding portions in the magnetic-substance plates 19, 21 and 23 and 25 so as to fitted in the above grooves, whereby the positioning means may be provided. Of the magnetic-substance plates 19, 21 and 23 and 25, central ones 21, 23 adjacent to each other are disposed in a back-to-back relationship so as to have their flat-side or back surfaces 21C, 23C abut against each other and welded to each other. In this case, it is possible to position the annular bobbins 15, 17 relative to each other at the same time when the magnetic-substance plates 19, 21, 23, 25 are positioned relative to the annular bobbins 15, 17. Consequently, the magnetic-substance plates 21, 23 having their back surfaces 21C, 23C welded to each other may function as the positioning means. It is also possible to use the magnetic-substance plates 21, 23 having their back surfaces 21C, 23C not welded to each other as shown in Fig. 10. In this case, the annular bobbins 15 and 17 are provided with outer-peripheral projections 15B and 17B, respectively. In assembly operations, these projections 15B, 17B are fitted in a notched portion 1A of the casing 1 to form the positioning means. Incidentally, in this case, it is natural to form a notched portion 100A in the yoke segment 100, which notched portion 100A corresponds in position to the notched portion 1A of the casing 1 so as to receive the projections 15A, 17A therein in in the assembly operations. As is clear from the above description, after the magnetic-substance plates 19, 21 and 23, 25 are positioned relative to the annular bobbins 15 and 17, respectively, it is possible to position the annular bobbins 15, 17 relative to the casing 1 at the same time when these bobbins 15, 17 are positioned relative to each other, because the projections 15B, 17B are fitted in the notched portions 1A of the casing 1 by simply inserting the annular bobbins 15, 17 into the casing 1, which bobbins 15 and 17 have been provided with the magnetic-substance plates 19, 21 and 23, 25, respectively. Namely, in the embodiment of the present invention shown in Fig. 10, since various types of the positioning means may be provided therein, it is possible to manufacture the sensor of the present invention in an easy manner with high accuracy in positioning of the stator coils, which improves the sensor of the present invention in measuring accuracy. Figs. 11 and 12 show another type of the positioning means, which will be now described with reference to the drawings. In this type of the positioning means shown in Figs. 11 and 12, an annular bobbin 150 is provided with a pair of annular grooves 151, 152 which axially overlap each other and are wound with the stator coils (not shown). In contrast with the other types of the positioning means having been described above, in this type of the positioning means, as shown in Figs. 11 and 12, there are provided a pair of magnetic-substance plates 153, 154. The magnetic-substance plate 153 is provided with a cylindrical yoke portion 153a for covering the outer peripheral surfaces of the two stator coils (not shown). Formed in a lower-end portion of the cylindrical yoke portion 153a of the magnetic-substance plate 153 are four pawl portions 155 two of which are shown in Fig. 11. On the other hand, the remaining magnetic-substance plate 154 is provided with four grooves 156 for receiving the four pawl portions 155 therein in assembly operations. In the assembly operations, first, the annular bobbin 150 is mounted in the cylindrical yoke portion 153a of the magnetic-substance plate 153. Then, the other magnetic-substance plate 154 is mounted on the magnetic-substance plate 153 from the bottom of the plate 153, so that the four pawl portions 155 of the magnetic-substance plate 153 are fitted in the grooves 156 of the other magnetic-substance plate 154, whereby a bobbin assembly 161 shown in Fig. 12 is completed. This bobbin assembly 161 combines with a core assembly 163 to form a single unit which is fitted in the casing (not shown), so that the sensor of the present invention is completed through the assembly operations. In this case, the pawl portions 155 and the grooves 156 are formed into the positioning means. Incidentally, the core assembly 163 is constructed of a rotating shaft, a rotating core member and the like, details of which are omitted in Fig. 12. It has been already checked that the sensor of the present invention having the above construction can detect the substantially effective variations of the inductance. In this case shown in Figs. 11 and 12, since the number of the magnetic-substance plates 153, 154 is two, it is easy to accomplish the positioning of these plates 153, 154. Consequently, it is possible to manufacture the sensor of the present invention excellent in measuring accuracy in an easy manner, provided that the annular bobbin 150 has been already positioned relative to the magnetic-substance plates 153, 154. The positioning of the annular bobbin 150 relative to the magnetic-substance plates 153, 154 is accomplished as follows: For example, a pair of semicircular notched portions 171 are formed in an upper surface (as viewed in Fig. 11) of the magnetic-substance plate 153. On the other hand, a pair of slightly-flat upright pieces 172 are formed in an upper surface of the annular bobbin 150, and fitted in the notched portions 171 of the magnetic-substance plate 153. In addition to the above, four upright pieces (not shown), which are similar in shape to the upright pieces 172, are also formed in a lower surface of the annular bobbin 150, and fitted in four semicircular notched portions 173 of the magnetic-substance plate 154 so as to accomplish the positioning of the annular bobbin 150 relative to the magnetic-substance plates 153, 154.

Claims: Sensor for contactless determination of an angle of rotation of a rotatable structural element, with a rotor (10, 50) provided with a magnetic-substance element (9, 31, 33, 49) arranged asymmetrically with respect to an axis of rotation of the rotor (10, 50), and with a first and a second annular stator coil (11, 13, 51, 53) arranged coaxially with respect to the rotor (10, 50), so that the angle of rotation can be measured by means of one of the stator coils (11, 13, 51, 53), characterized in that a magnetic-circuit member (19, 21, 23, 25, 59, 63) is provided which forms a yoke or core means for each of the stator coils (11, 13, 51, 53), wherein the magnetic-circuit member (19, 21, 59) for the first stator coil (11, 51) has an asymmetric shape with respect to the axis of rotation of the rotor (10, 50), so as to approach the magnetic-substance element (9, 31, 49) of the rotor (10, 50) only when the angle of rotation of the rotor (10, 50) is in a first angular range, whereby the magnetic-substance element (9, 31, 49) of the rotor (10, 50) functions as a part of the magnetic circuit of the first stator coil (11, 51), and wherein the magnetic-circuit member (23, 25, 63) for the second stator coil (13, 53) has an asymmetric shape with respect to the axis of rotation of the rotor (10, 50), so as to approach the magnetic-substance element (9, 33, 49) of the rotor (10, 50) only when the angle of rotation of the rotor (10, 50) is in a second angular range outside the first angular range, whereby the magnetic-substance element (9, 33, 49) of the rotor (10, 50) functions as a part of a magnetic circuit of the second stator coil (13, 53). Sensor according to claim 1, characterized in that rotations of the rotor (10, 50) are detectable as variations in voltage issued from the terminals of the stator coils (11, 13) due to variations of the stator coils (11, 13, 51, 53) in inductance, that the first stator coil (11) is sandwiched between a pair of first magnetic-circuit forming members (19, 21) in a direction parallel to the axis of rotation of the rotor (10). wherein each of the magnetic-circuit forming members (19, 21) is made of a magnetic substance and has an annular shape having its inner peripheral portion partially flanged to form an inner protruding flanged portion (19A, 21A) with a predetermined degree measure of central angle. wherein each inner protruding flanged (19A, 21A) portion is spaced a minute clearance away from the rotor (10) when the rotor (10) rotates to approach the inner protruding flanged portion (19A, 21A) of each of the first magnetic-circuit forming member, (19, 21), and that the second stator coil (13) is sandwiched between a pair of second magnetic-circuit forming members (23, 25) in a direction parallel to the axis of rotation of the rotor (10), wherein each of the magnetic-circuit forming members (23, 25) is made of a magnetic substance and has an annular shape having its inner peripheral portion partially flanged to form an inner protruding flanged portion (23A, 25A) with a predetermined degree measure of central angle, wherein each inner protruding flanged portion (23A, 25A) is spaced a minute clearance away from the rotor (10) when the rotor (10) rotates to approach the inner protruding flanged portion (23A, 25A) of each of the second magnetic-circuit forming members (23, 25), wherein the inner protruding flanged portions (19A, 21A) of the first magnetic-circuit forming (19, 21) members do not overlap the inner protruding flanged portions (23A, 25A) of the second magnetic-circuit forming members (23, 25) in a direction parallel to the axis of rotation of the rotor (10). Sensor according to claim 2, characterized in that the inner protruding flanged portions (19A, 21A, 23A, 25A) extend parallel to the axis of rotation of the rotor (10), that the inner protruding flanged portions (19A, 21A) of the first magnetic-circuit forming members (19, 21) are spaced in axial direction of the rotor (10), and that the inner protruding flanged portions (23A, 25A) of the second magnetic-circuit forming members (23, 25) are spaced in axial direction of the rotor (10). Sensor according to any one of the preceding claims. characterized in that the magnetic-substance element (9, 31, 33, 49) of the rotor (10, 50) has a semicylindrical shape, wherein a center axis thereof coincides with the rotational axis of the rotor (10, 50). Sensor according to claim 3, characterized in that the magnetic-substance element (9, 31, 33, 49) of the rotor (10) is constructed of a pair of parallel semicircular plate members (31, 33), wherein the center axis of each plate member (31, 33) coincides with the rotational axis of the rotor (10), that the semicircular plate members (31, 33) are fixedly mounted on the rotor (10) spaced in axial direction of the rotor (10), that one of the semicircular plate members (31, 33) has its outer peripheral portion with a predetermined degree measure of central angle spaced a minute clearance away from each of the inner protruding flanged portions (19A, 21A) of the first magnetic-circuit forming members (19, 21) and positioned therebetween, when the rotor (10) rotates to approach the inner protruding flanged portions (19A, 21A) of the first magnetic-circuit forming members (19, 21), and that the other of the semicircular plate members (31, 33) has its outer peripheral portion with a predetermined degree measure of central angle spaced a minute clearance away from each of the inner protruding flanged portions (23A, 25A) of the second magnetic-circuit forming members (23, 25) and positioned therebetween, when the rotor (10) rotates to approach the inner protruding flanged portions (23A, 25A) of the second magnetic-circuit forming members (23, 25). Sensor according to any one of the preceding claims, characterized in that the stator coils (11, 13, 51, 53) are spaced from each other in a direction parallel to an axis of rotation of the rotor (10, 50) by a predetermined clearance. Sensor according to claim 6, characterized in that the magnetic-substance element (49) of the rotor (50) has a semicircular plate shape. wherein the center axis thereof coincides with the rotational axis of the rotor (50), and wherein the magnetic-substance element (49) is fixedly mounted on the rotor (50) so as to pass through the space between the statoi coils (51, 53), when the rotor (50) rotates, that a first core member (59), which is made of a magnetic substance and has a predetermined degree measure of central angle with respect to the rotational axis of the rotor (50), is fixedly mounted on an inner peripheral surface of the first stator coil (51), that a second core member (63), which is made of a magnetic substance and has a predetermined degree measure of central angle with respect to the rotational axis of the rotor (50), is fixedly mounted on an inner peripheral surface of the second stator coil (53), wherein the second core member (63) is disposed such that it does not overlap the first core member (59) in axial direction of the rotor (50), that a first magnetic shielding plate member (61) made of an electrically conductive material is provided and fixedly mounted on an axially inner surface of the first stator coil (51) in opposing relation to the second core member (63) with respect to the axial direction of the rotor (50), and that a second magnetic shielding plate member (65) made of an electrically conductive material is provided and fixedly mounted on an axially inner surface of the second stator coil (53) in opposing relation to the first core member (59) with respect to the axial direction of the rotor (50). Sensor according to any one of the preceding claims, characterized in that one or two bobbins (15, 17, 55, 57) are provided on which the stator coils (11, 13, 51, 53) are wound, that a plurality of magnetic-substance plates (19, 21, 23, 25) are provided, wherein a pair thereof sandwich each bobbin (15, 17, 55, 57) therebetween, that the rotor (10, 50) axially passes through the magnetic-substance plates (19, 21, 23, 25) and the one or two bobbins (15, 17, 55, 57), that a casing (1, 41) is provided which contains the one or two bobbins (15, 17, 55, 57), the stator coils (11, 13, 51, 53), the magnetic-substance plates (19, 21, 23, 25) and the rotor (10, 50) therein, and that at least a positioning means is provided between a pair of magnetic-substance plates (19, 21, 23, 25) to position these relative to each other. Sensor according to claim 8, characterized in that a plurality of positioning means is provided, wherein the one or two bobbins (15, 17, 55, 57), the magnetic-substance plates (19, 21, 23, 25) and the casing (1, 41) are separated and positioned relative to cach other by the positioning means. Sensor according to claim 9, characterized in that the positioning means provided between the magnetic-substance plates (19, 21, 23, 25) and the bobbins (15, 17, 55, 57) comprise an axially extending portion formed in an inner peripheral portion of one of opposite axial surfaces of each bobbin (15, 17, 55, 57), wherein each bobbin (15, 17, 55, 57) has an annular shape, and an axially extending portion formed in an inner peripheral portion of one of opposite axial surfaces of each magnetic-substance plate (19, 21, 23, 25), wherein each magnetic-substance plate (19, 21, 23, 25) has an annular shape, and wherein each of the axially extending portions of the bobbins (15, 17, 55, 57) is fitted to the inner peripheral portion of each annular magnetic-substance plate (19, 21, 23, 25), while the axially extending portion of each magnetic-substance plate (19, 21, 23, 25) is fitted to the inner peripheral portion of each bobbin (15, 17, 55, 57). Sensor according to claim 9, characterized in that the positioning means provided in bobbins (15, 17, 55, 57) is constructed of adjacent magnetic-substance plates (19, 21, 23, 25), which sandwich each bobbin (15, 17, 55, 57) therebetween, wherein the adjacent magnetic-substance plates (19, 21, 23, 25) are integrated into one piece. Sensor according to claim 9, characterized in that the positioning means provided between each of the bobbins (15, 17, 55, 57) and the casing (1, 41) is constructed of a projection forming an outer peripheral surface of each bobbin (15, 17, 55, 57) and is constructed of a notch made on the casing (1, 41), wherein the notch is fitted in the projection of each bobbin (15, 17, 55, 57) in assembled condition.

Inventors: NAGASAKI WATARU, SHIMODA KAZUHIKO, TAKAHASHI HAJIME, TOGASHI KEN, NAGASAKI, WATARU, SHIMODA, KAZUHIKO, TAKAHASHI, HAJIME, TOGASHI, KEN
Applicants: ZEXEL CORP, ZEXEL CORPORATION
Application year: 1994
Main classification: G01D5
IPC codes: G01D5, G01B7